This invention relates to a watch dial and, more particularly, to a watch dial having a photosensitive plastic layer upon which a surface design, letter, window, symbol, picture or mark is formed and which photosensitive layer has been metal plated, as well as a process for manufacturing such a watch dial.
Currently, there is a multitude of designs for watch dials and there is a great demand to produce many different designs in small quantities as speedily as possible. Because of such demand for so many kinds of watch dial designs, the cost of the production and manufacturing of each design has become of significant importance.
Generally, there are three types of metal-based watch dials made today, namely, (1) a printed metal-based dial which has been surface treated, coated and printed; (2) a metal-based dial on which letters, symbols or the like are formed by implanting them on the dial base, finishing with a surface treatment, and then coating and printing; and (3) dials made by coining in which a metal base finished with a surface treatment and coated is stamped using a coining method to obtain a raised symbol and thereby having the symbols and the dial base formed in one body. These three kinds of prior art manufacturing of dials are described below:
With respect to the printed dial, there are generally two (2) manufacturing methods: (1) the Butler-finishing method which presents a hairline design; and (2) a radial design method which utilizes a stamping or pressing process.
The Butler-finishing method starts with a nickel copper alloy base plate shown at FIG. 1-A as base plate 1. Then feet 2 are provided on the base plate 1. Two methods are presently used for providing feet on the base plate. The first method utilizes silver wax and in which feet 2 made of a copper pipe filled with silver wax are implanted in the base plate 1. The base plate and the feet are maintained at 800.degree. C. for five (5) minutes in a furnace until the silver wax within the copper pipe melts and the feet are fixed on base 1. The disadvantage of this method is that the very high temperature (800.degree. C.) for melting the silver wax causes the material of base 1 to become dull. In the case of a base made of brass, the hardness of the base before heating to 800.degree. C. in the furnace is 180 Hv in Vickers hardness, whereas the hardness is reduced to 80 Hv after the base is maintained in a furnace. Therefore, one is limited in the thickness which may be used for the base plate and, in the case of brass, 30/100 mm is the thinnest base plate which may be practically used. A still further disadvantage of this method is that the high temperature requires a large and expensive furnace.
The second method for fixing the feet on the base is the use of resistance welding. By this method feet 2 having a sharpened end of dull copper are welded to the base 1 by applying electric current between the feet and the base while some pressure is subjected thereto. The principle of this method is that because of the resistance of the sharpended end portion of the feet is very large, the end portion is specially heated and the feet are fixed to the base. By this method, only the end portion of the feet 2 is heated and such a local heating does not effect the hardness of the base 1. However, this resistance welding methond has the disadvantage in that the feet and the base are subjected to pressure to ensure the stable fixation of the feet to the base, thereby causing the opposite side of the base to the feet to have projections as high as 10 to 20 mm. Thus, this method has the disadvantage that an additional process is required to remove the aforesaid projection on the base plate on the surface opposite the feet.
After fixing feet 2 on base 1 by either of the above two (2) methods in regard to the printed dial, the surface of the base plate is polished with a feather-cloth. If the polishing with the feather-cloth is incomplete and even if very small streaks are left on the surface, the appearance of the surface will be spoiled. Thus, the feature-cloth polishing process requires the skill of a highly-trained person. If there is a material fault in the base plate such as an impurity, it becomes nearly impossible to obtain a perfectly polished surface. Thus, the base plate must be made of a special metal including very little impurtities and must be carefully refined.
At this point the Butler design is provided on the polished surface of the base by a specific processing machine. Ten patterns of the Butler design are now available such as a radical design, a hairline design and the like and different processing machines are required for each design.
In FIG. 1-C the result of the providing a Butler design is shown. The surface is then honed by a specific honing machine and is followed by metal plating such as with nickel, silver or gold and such plating is then followed by the final step of spray coating 3 and printing as shown in FIG. 1-D.
The stamping method for manufacturing the printed dial begins with a press-cut base 1 which is annealed in order to facilitate the stamping process which is to follow. In accordance with this method, the design is provided on the surface of base 1 by the stamp process using a friction press of about 100 tons. Such friction press is a rather large and heavily equipped machine for the processing of a small dial. Following the stamping, a center hole is formed in base 1 by press-flanking. Feet are then provided by the above mentioned silver wax method. The resistance welding cannot be used since the surface of the base has already been stamped with a pattern and therefore it would not be feasible to remove projections which are formed in the course of the resistance welding method. Following the fixing of the feet, the base is plated, coated and printed in order to obtain the finished printed dial.
The second known process for manufacturing a watch dial involves an implanted dial. In this process, the base is prepared as above and the letters, marks, windows or the like are implanted in the base. Referring to FIG. 3 the letters 4 and marks to be implanted have feet 4a and corresponding holes must be provided on the base. If a window is to be implanted, the dial base is provided with an opening corresponding to the window. The implanted letters, marks, window or like are then fixed to the base plate by use of caulking together with an injected adhesive agent. Usually in this process there is as many as 11 or 12 implanted letters and thus the cost of the additional parts can be substantial. A further problem with the implanted method is that it involves many extra steps and is difficult to automate thus requiring many hand operations by a highly skilled worker.
The third known process for manufacturing a watch dial is the coining process and is described in reference to FIG. 2. In this process the base plate and feet are prepared as in the printed dial process and a design is printed, plated and coated on the base plate. In the coining method this is followed by the use of a press die to form raised letters as shown in FIG. 2-A. The raised letters are then finished by a diecut (FIG. 2-B) followed by printing and plating on the diecut surface. Thus the dial and letters are formed in one body and the coining process does not require the degree of skill as the other methods. However, the coining method has two (2) major disadvantages. First, the production of metal dies for the forming of the raised letters is expensive. This presents a particular problem when the number of dials to be produced is relatively small. The second disadvantage is that since the dial and the letters are formed in one body it is often too difficult, if not impossible, to diecut complicated designs.